Abstract: An all DC offshore wind farm is one of the important technologies for the development of large-scale long-distance offshore wind energy. The high-voltage DC/DC transformer, which interconnects the medium-voltage collection system and the high-voltage transformation system, plays the pivotal role in tackling the challenges, such as the high voltage stress, the large current stress, and the high step-up ratio. This paper proposes a hybrid modular high-voltage DC/DC transformer with the submodule strings, the diodes, and the thyristors. The submodule strings are connected in parallel to the medium voltage DC port sharing large current stress and in series to the high voltage DC port assuming high voltage stress respectively. The diodes and thyristors play the auxiliary role to realize the commutation between the parallel and the series systems. Compared with the other high-voltage DC/DC transformers, the proposed topology is characterized in its high efficiency, light weight, and low installation capacity. In addition, the fault characteristics and the fault current clearing of a commutation failure caused by an irreliable thyristor are analyzed. The feasible strategies of the fault ride-through are proposed to improve the topology's reliability. The affecting factors and the parameter selection of the fault ride-through processing are studied. At last, the effectiveness of the proposed topology and the ride-through strategy are verified by simulation and experiment.